A377364 a(n) = least k such that 2n*3^k-2 is prime, or 0 if no prime is reached.

1, 1, 1, 2, 1, 1, 1, 3, 2, 1, 1, 1, 1, 3, 2, 1, 1, 1, 4, 5, 1, 2, 1, 2, 1, 1, 1, 9, 2, 1, 4, 1, 1, 2, 1, 5, 1, 1, 11, 1, 2, 2, 4, 3, 1, 1, 1, 3, 2, 4, 1, 1, 5, 3, 1, 1, 3, 1, 2, 4, 1, 1, 1, 2, 2, 1, 5, 1, 3, 1, 2, 1, 1, 8, 3, 1, 1, 4, 2, 80, 1, 6, 1, 8, 2, 2

Offset

1,4

Links

Table of n, a(n) for n=1..86.

Example

a(20) = 5 because 40*3^5 + 1 is prime and 40*3^k + 1 is not prime for k=1..4.

Mathematica

{b, h} = {3, 2}; f[n_, k_] := n*b^k - h
s[n_] := Select[Range[20], PrimeQ[f[n, #]] &, 1]
Flatten[Table[s[n], {n, 1, 200}]]

Crossrefs

Cf. A000040, A050412, A354747, A377365, A377366, A377367.

Sequence in context: A278113 A242012 A359165 * A086290 A136568 A342477

Adjacent sequences: A377361 A377362 A377363 * A377365 A377366 A377367

Keyword

nonn

Author

Clark Kimberling, Oct 31 2024

Status

approved